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# a solution for N=1000 to
# https://projecteuler.net/problem=14
# we use a fast local array to
# memoize small collatz numbers
export
function $test() {
@start
%mem =l alloc4 4000
@loop
%n =w phi @start 1, @newm %n9, @oldm %n9
%cmax =w phi @start 0, @newm %c, @oldm %cmax
%fin =w csltw %n, 1000
jnz %fin, @cloop, @end
@cloop
%n0 =w phi @loop %n, @odd %n2, @even %n3
%c0 =w phi @loop 0, @odd %c1, @even %c1
%no1 =w cnew %n0, 1
jnz %no1, @iter0, @endcl
@iter0
%ism =w csltw %n0, %n
jnz %ism, @getmemo, @iter1
@iter1
%c1 =w add %c0, 1
%p =w and %n0, 1
jnz %p, @odd, @even
@odd
%n1 =w mul 3, %n0
%n2 =w add %n1, 1
jmp @cloop
@even
%n3 =w shr %n0, 1
jmp @cloop
@getmemo # get the count for n0 in mem
%n0l =l extsw %n0
%idx0 =l mul %n0l, 4
%loc0 =l add %idx0, %mem
%cn0 =w loadw %loc0
%c2 =w add %c0, %cn0
@endcl # store the count for n in mem
%c =w phi @getmemo %c2, @cloop %c0
%nl =l extsw %n
%idx1 =l mul %nl, 4
%loc1 =l add %idx1, %mem
storew %c, %loc1
%n9 =w add 1, %n
%big =w cslew %cmax, %c
jnz %big, @newm, @oldm
@newm
jmp @loop
@oldm
jmp @loop
@end
storew %cmax, $a
ret
}
# >>> driver
# extern void test(void);
# int a;
# int main() { test(); return !(a == 178); }
# <<<
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